rebar3: Update to 3.19.0

Changelog taken from https://github.com/erlang/rebar3/releases

3.19.0

New features:
    Add --offline option and REBAR_OFFLINE environment variable
    Add support for project-local plugins in umbrella projects only
    Add eunit --test flag

Experimental features for which we promise no backwards compatibility in
the near future:
    Experimental vendoring provider
        Support plugins in experimental vendor provider

Other changes:
    Support OTP 23..25 inclusively
    Bump Relx to 4.7.0
        Use erlexec directly in relx helper functions
        Make rlx_util:parse_vsn parse integer versions
        fix awk script check_name() in extended_bin
        avoid crash when overlay is malformed
        keep attributes when stripping beams
        Fix {include_erts,true} in Windows releases
        ensure the erl file is writable before copying dyn_erl to it
        Various tests added
    Properly carry overlay_vars settings for files in relx
    Track mib compilation artifacts
    Attempt to find apps in git subdirs (sparse checkouts)
    Do not discard parameters --system_libs and --include-erts when duplicate values exist
    Use default depth parameter for SSL
    Fix global cache config overriding
    Error out on unknown templates in 'new' command
    Fix a typo
    Bump certifi to 2.9.0
    add a debug message in internal dependency fetching code
    Use SPDX id for license in template and test
    Use default branch for git and git_subdir resources with no revision

(nikita)